Yahoo! Messenger is a popular advertisement-supported instant messaging client and associated protocol provided by Yahoo!. Yahoo! Messenger is provided free of charge and can be downloaded and used with a generic "Yahoo! ID" which also allows access to other Yahoo! services, such asYahoo! Mail, where users can be automatically notified when they receive new email. Yahoo! also offers PC-PC, PC-Phone and Phone-to-PC service, file transfers, webcam hosting, text messaging service, and chat rooms in various categories.

Yahoo! Messenger was originally launched under the name Yahoo! Pager on 1998-03-09.

In addition to instant messaging features similar to those offered by ICQ, it also offers (on Microsoft Windows) features such as: IMVironments (customizing the look of Instant Message windows, some of which include authorized themes of famous cartoons such as Garfield or Dilbert), address-book integration and Custom Status Messages. It was also the first major IM client to feature BUZZing and music-status. Another recently added feature is customized avatars.

Chat

All versions of Yahoo! Messenger have included the ability to access Yahoo! Chat rooms.

On June 19, 2005, with no advance warning, Yahoo! disabled users' ability to create their own chat rooms. The move came after KPRC-TV in Houston, Texas reported that many of the user-created rooms were geared toward pedophilia. Many regulars in these rooms used the rooms to set up meetings to have sex with children and trade lewd pictures. While it was thought this move came as a result of several advertisers pulling their ads from Yahoo!, a more likely cause was a $10 million lawsuit filed by watchdog groups of internet portals on behalf of a 12-year-old victim of molestation.

Yahoo! has since closed down the chat.yahoo.com site (which is now a redirect to a section of the Yahoo! Messenger page) because the great majority of chat users accessed it through Messenger. In August of 2007, it began requiring word verification in order to use Yahoo! Chat. Officially, this is to guard against spammers and automated bots, which had been a source of frustration for many chatters (This method has proved highly unsuccessful, as many rooms now have more bots than users). However, as this also logs users' IP addresses, this feature could presumably be used to monitor against the type of behavior that prevailed in the pedophilia-oriented rooms. The company claims to be still working on a way to allow users to create their own rooms while providing safeguards against abuse.